1. Field of the Invention
The present invention relates to an image forming apparatus which performs an image forming operation on continuous printing sheet wound in a roll shape, and a control method thereof.
2. Description of the Related Art
Currently, a roll paper printer which performs an image forming operation on continuous printing paper wound in a roll shape (roll paper) has merits of high degrees of freedom in an output size (image forming length), low cost of roll paper, and the like. On the other hand, in the roll paper printer, since a curl unique to the roll paper is required to be removed, a printer engine includes a curl correction unit. In the roll paper printer, since the curl correction unit forms a curl in an opposing direction during the image forming operation, the curl unique to the roll paper is removed. The image-forming processed printing paper, the curl of which has been removed by the curl correction unit, is cut by a cutter and is discharged outside the printer, while the remaining paper is rolled up and stored in a cartridge.
When an electric power failure, forced termination, battery dead state, or the like has occurred during the image forming operation of the roll paper printer, and a power supply is stopped, paper in the middle of the image forming operation may remain in the printer engine. When a power supply is turned on again from this state, an image forming operation may be unwantedly restarted from a position on the paper in the middle of the image forming operation. When the image forming operation is restarted from the position on the paper in the middle of the image forming operation, not only image forming quality impairs, but also a peeling error of an ink sheet occurs in case of a thermal transfer printer, thereby causing jamming of the paper and ink sheet.
In order to prevent such problems, when the paper remains in the printer engine upon power-ON, processing for discharging the remaining paper is executed.
For example, Japanese Patent Laid-Open No. 2008-137226 describes that a roll paper printer includes a storage unit which stores an image forming status, a previous image forming status is referred to from image forming statuses stored in the storage unit upon power-ON, and when the previous image forming status indicates that the previous image forming operation was incomplete, printing paper is cut by a maximum image forming length based on the length of an ink sheet and is discharged.
The roll paper printer normally includes the curl correction unit used to correct a roll-shaped curl. When the curl correction unit holds paper for a predetermined time period or longer, a curl in the opposing direction is locally formed on the paper. When an image forming operation is performed using the paper with such curl, not only the local curl remains on the paper, but also image forming quality on a curl region lowers.
Since Japanese Patent Laid-Open No. 2008-137226 adopts the method of clipping printing paper by the maximum image forming length based on the length of the ink sheet, the paper may be clipped before the curl region.
By contrast, when paper is cut by adding a length from an image forming unit such as a thermal head to the curl correction unit to the maximum image forming length, a portion formed with the curl can be removed, thereby solving the above problem.
However, when the paper is cut by adding the length from the image forming unit to the curl correction unit to the maximum image forming length, the paper clipping amount increases, thereby decreasing the number of sheets that can undergo image forming operations.